CN114225710A

CN114225710A - Viscoelastic composite membrane and preparation method and application thereof

Info

Publication number: CN114225710A
Application number: CN202111591290.8A
Authority: CN
Inventors: 王艳; 朱腾阳; 柴政泽
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2021-12-23
Filing date: 2021-12-23
Publication date: 2022-03-25
Anticipated expiration: 2041-12-23
Also published as: CN114225710B

Abstract

The invention discloses a viscoelastic composite membrane and a preparation method and application thereof, belonging to the field of membrane separation. Dissolving polydimethylsiloxane in an organic solvent, and then adding a cross-linking agent to enable the polydimethylsiloxane to generate a cross-linking reaction; by controlling the addition amount of the cross-linking agent, a low cross-linking density polydimethylsiloxane viscous solution with the low cross-linking density of 1 multiplied by 10 is obtained^‑4mol/mL‑3×10^‑4mol/mL; the low crosslink density polydimethylsiloxane is made into a viscous stateAnd (4) blade-coating the solution on the supporting layer, and volatilizing the organic solvent to obtain the viscoelastic composite membrane. The viscoelastic composite membrane regulates the crosslinking density of polydimethylsiloxane by controlling the addition amount of the crosslinking agent, obtains polydimethylsiloxane viscous fluid with low crosslinking density, is obtained by blade coating, and is applied to pervaporation organic matter recovery. The viscoelastic selective layer has higher molecular chain flexibility and large free volume, and shows ultrahigh permeation flux compared with the traditional polydimethylsiloxane elastic membrane.

Description

Viscoelastic composite membrane and preparation method and application thereof

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to a viscoelastic composite membrane and a preparation method and application thereof.

Background

A conventional polydimethylsiloxane elastic composite membrane is a polymer membrane commonly used in membrane separation processes. Because polydimethylsiloxane has strong hydrophobicity, the polydimethylsiloxane elastic composite membrane has been widely researched and used for pervaporation organic matter recovery. In the patent with publication number CN 104069751 a, a preparation method of PDMS/PTFE pervaporation hollow fiber membrane is disclosed, which is used for separating acetone/butanol/ethanol solution in fermentation broth, but has the disadvantages of long preparation period, difficult storage of prepared casting membrane solution and high preparation energy consumption. In addition, the permeation flux of the hollow fiber membrane for organic recovery was about 0.3kg/m²h, not enough for industrial applications. Therefore, how to efficiently prepare a polydimethylsiloxane thin film composite membrane with high permeation flux is a problem faced at present.

Disclosure of Invention

The invention solves the technical problems of long preparation period, difficult storage of casting solution, high preparation energy consumption, poor separation performance and low permeation flux of the polydimethylsiloxane elastic composite membrane in the prior art. In order to solve the technical problems, the invention adopts the cross-linking agent with high reactivity, shortens the film preparation period, reduces the high-temperature post-treatment process of further cross-linking after film preparation, and reduces the energy consumption of film preparation. In addition, the addition amount of the cross-linking agent is controlled, the cross-linking density of the polydimethylsiloxane is regulated and controlled, the casting solution which is stored stably is obtained, and the polydimethylsiloxane viscoelastic composite membrane is obtained by blade coating, so that the main problems existing in the traditional polydimethylsiloxane elastic membrane at present are solved.

According to the first aspect of the present invention, a method for preparing a viscoelastic composite membrane is provided, wherein polydimethylsiloxane is dissolved in an organic solvent, and then a cross-linking agent is added to cause the polydimethylsiloxane to perform a cross-linking reaction; the addition amount of the cross-linking agent is controlled to enable the polydimethylThe siloxane has low crosslinking density, and the low crosslinking density is 1 multiplied by 10 to obtain the low crosslinking density polydimethylsiloxane viscous solution^-4 mol/mL-3×10^-4mol/mL; and (3) coating the low crosslinking density polydimethylsiloxane viscous solution to a supporting layer by blade coating, and volatilizing an organic solvent to obtain the viscoelastic composite membrane.

Preferably, the phase angle of the viscoelastic composite film is 15 ° to 75 °.

Preferably, the phase angle of the viscoelastic composite film is 30 ° to 45 °.

Preferably, the polydimethylsiloxane is amino-terminated polydimethylsiloxane, the cross-linking agent is a monomer containing an acid chloride group, and the monomer containing the acid chloride group is dissolved and then added into the amino-terminated polydimethylsiloxane solution; the mass ratio of the amino-terminated polydimethylsiloxane to the monomer containing the acyl chloride group is (350) -470) 1;

preferably, the concentration of the monomers containing acid chloride groups after dissolution is from 0.05 to 2% by weight;

preferably, the monomer containing acyl chloride group is trimesic acid chloride, isophthaloyl dichloride, succinoyl chloride or trans-5-norbornyl-2, 3-diformyl chloride.

Preferably, the polydimethylsiloxane is hydroxyl-terminated polydimethylsiloxane, the crosslinking agent is a silane coupling agent containing ethoxy or methoxy, and the catalyst for the crosslinking reaction is dibutyltin dilaurate; the mass ratio of the hydroxyl-terminated polydimethylsiloxane to the silane coupling agent is (99-399) to 1;

preferably, the silane coupling agent containing an ethoxy group is tetraethoxysilane, vinyltris (2-methoxyethoxy) silane, triethoxyfluorosilane, benzyltriethoxysilane, pentyltriethoxysilane, phenyltriethoxysilane, octadecyltriethoxysilane, or vinyltriethoxysilane; the silane coupling agent containing methoxyl group is (3-mercaptopropyl) trimethoxysilane, 3-glycidoxypropyltrimethoxysilane, octyltrimethoxysilane, trimethyloxyphenylsilane or vinyltrimethoxysilane.

Preferably, the polydimethylsiloxane is vinyl-terminated polydimethylsiloxane, the crosslinking agent is siloxane containing silicon hydrogen bonds, and the catalyst for the crosslinking reaction is chloroplatinic acid or [1, 3-dicyclohexyl-imidazol-2-yl ] [1, 3-divinyl-1, 1,3,3, -tetramethyldisiloxane ] platinum (0); the mass ratio of the vinyl-terminated polydimethylsiloxane to the siloxane containing the silicon-hydrogen bond is (99-399) to 1;

preferably, the siloxane containing silicon hydrogen bonds is poly (methylhydrosiloxane).

According to another aspect of the present invention, there is provided a viscoelastic composite film prepared by any one of the methods.

Preferably, the viscoelastic composite film comprises a support layer and a viscoelastic selective layer, wherein the viscoelastic selective layer is coated on the surface of the support layer in a blade coating mode; the viscoelastic selective layer is polydimethylsiloxane with low crosslinking density, specifically 1 × 10^-4mol/mL-3×10^-4mol/mL; the supporting layer is a polymer film, or the supporting layer is non-woven fabric coated with the polymer film in a scraping mode, or the supporting layer is an inorganic film.

According to another aspect of the present invention, there is provided a use of the viscoelastic composite film for separating an organic solvent from a mixed solvent miscible with water.

Preferably, the water-miscible organic solvent is ethanol, methanol, isopropanol, ethyl acetate, acetone, ethylene glycol or butanol;

preferably, the temperature of the separation is 30 ℃ to 80 ℃;

preferably, the mass concentration of the organic solvent in the mixed solvent is 1 wt% to 10 wt%.

Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

(1) the invention designs a new membrane type, and improves the separation performance (such as ethanol) of the polydimethylsiloxane elastic membrane for separating the organic solvent from the mixed solvent which is mutually dissolved with water by improving the flexibility and the free volume of a polymer molecular chain.

(2) The high-reactivity crosslinking agent is selected and used as a monomer containing acyl chloride groups, so that the membrane preparation period is remarkably shortened; meanwhile, the high-temperature post-treatment process of further crosslinking after film forming is reduced, and the energy consumption for film forming is reduced.

(3) According to the invention, the addition amount of the cross-linking agent is controlled, so that the cross-linking density of the polydimethylsiloxane is adjusted, and the polydimethylsiloxane casting solution capable of being stably stored is obtained.

(4) The polydimethylsiloxane viscoelastic composite membrane with high separation efficiency is obtained by optimizing the crosslinking density of the polydimethylsiloxane. Preferred polydimethylsiloxanes with low crosslink densities have flexible molecular chains and large free volumes. Compared with the polydimethylsiloxane elastic membrane composite membrane, the permeation flux of the polydimethylsiloxane viscoelastic composite membrane is improved by 453 percent under the same test condition.

Drawings

FIG. 1 is an infrared spectrum of an amino terminated polydimethylsiloxane and viscoelastic composite film of example 3.

Fig. 2 is a phase angle (δ) and tan δ of the composite films prepared in comparative example 1, comparative example 2 and example 3.

Fig. 3 is a phase angle (δ) and tan δ of the composite films prepared in example 1, example 2, example 3, example 4, example 5 and example 6.

FIG. 4 shows swelling degree test results of composite films of comparative example 1, comparative example 2 and example 3.

Fig. 5 is the results of the pervaporation test on the composite membranes of comparative example 1, comparative example 2 and example 3.

Fig. 6 is the results of pervaporation tests on viscoelastic composite membranes of example 1, example 2, example 3, example 4, example 5, and example 6.

FIG. 7 is a graph showing the time taken for the viscosity of the casting solutions of comparative example 1, comparative example 2 and example 3 to reach 150 mPas.

FIG. 8 is the change in viscosity of the casting solution of example 3 with storage time.

FIG. 9 is a graph of the effect of post-treatment temperature on pervaporation performance after preparation of viscoelastic composite films according to example 3.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention relates to a preparation method of a viscoelastic composite membrane, which comprises the steps of dissolving dimethyl silicone polymer in a volatile organic solvent, and then adding a cross-linking agent to enable the dimethyl silicone polymer to generate a cross-linking reaction; the polydimethylsiloxane viscous solution with low crosslinking density of 1 multiplied by 10 is obtained by controlling the addition amount of the crosslinking agent^-4mol/mL-3×10^-4mol/mL; and (3) coating the low crosslinking density polydimethylsiloxane viscous solution to a supporting layer by blade coating, and volatilizing the organic solvent to obtain the viscoelastic composite membrane.

In some embodiments, the polydimethylsiloxane is present in an amount ranging from 10 wt% to 25 wt% in the volatile organic solvent.

In some embodiments, the polydimethylsiloxane has a number average molecular weight of 20,000g/mol to 500,000 g/mol.

In some embodiments, the volatile organic solvent is n-hexane, n-heptane, tetrahydrofuran, cyclohexane, chloroform, dichloromethane, or toluene.

In some embodiments, the polydimethylsiloxane is amino-terminated polydimethylsiloxane, the crosslinking agent is a monomer containing an acid chloride group, and the monomer containing the acid chloride group is dissolved and then added into the amino-terminated polydimethylsiloxane solution; the mass ratio of the amino-terminated polydimethylsiloxane to the monomer containing the acyl chloride group is (350) -470) 1;

In some embodiments, the polydimethylsiloxane is a hydroxyl-terminated polydimethylsiloxane, the crosslinking agent is a silane coupling agent containing ethoxy or methoxy groups, and the catalyst for the crosslinking reaction is dibutyltin dilaurate; the mass ratio of the hydroxyl-terminated polydimethylsiloxane to the silane coupling agent is (99-399) to 1;

preferably, the silane coupling agent containing an ethoxy group is tetraethoxysilane, vinyltris (2-methoxyethoxy) silane, triethoxyfluorosilane, benzyltriethoxysilane, pentyltriethoxysilane, phenyltriethoxysilane, octadecyltriethoxysilane, and vinyltriethoxysilane; the silane coupling agent containing methoxy group is (3-mercaptopropyl) trimethoxysilane, 3-glycidoxypropyltrimethoxysilane, octyltrimethoxysilane, trimethylsiloxyphenylsilane and vinyltrimethoxysilane.

In some embodiments, the polydimethylsiloxane is a vinyl-terminated polydimethylsiloxane, the crosslinking agent is a siloxane containing silicon-hydrogen bonds, and the catalyst for the crosslinking reaction is chloroplatinic acid or [1, 3-dicyclohexyl-imidazol-2-yl ] [1, 3-divinyl-1, 1,3,3, -tetramethyldisiloxane ] platinum (0); the mass ratio of the vinyl-terminated polydimethylsiloxane to the siloxane containing the silicon-hydrogen bond is (99-399) to 1;

preferably, the siloxane containing the silicon hydrogen bond is poly (methylhydrosiloxane), and the molecular weight of the poly (methylhydrosiloxane) is 1000g/mol-10000 g/mol.

The viscoelastic composite membrane prepared by the invention comprises a supporting layer and a viscoelastic selective layer, wherein the viscoelastic selective layer is coated on the surface of the supporting layer in a blade mode; the viscoelastic selective layer is polydimethylsiloxane with low crosslinking density; the supporting layer is a polymer film, or the supporting layer is non-woven fabric coated with the polymer film in a scraping mode, or the supporting layer is an inorganic film.

In some embodiments, the polymer membrane of the support layer is a polyacrylonitrile membrane, a polyethersulfone membrane, a polysulfone membrane, a polyimide membrane, a polyamide membrane, a polyetherimide membrane, a polyamideimide membrane, a cellulose acetate membrane, a cellulose triacetate membrane, or a polyvinylidene fluoride membrane; the inorganic film of the support layer is an aluminum oxide film, a cobalt oxide film, a silicon oxide film, an aluminum silicate film or a silicon carbide film.

In some embodiments, the nonwoven fabric coated with the drawdown polymer film is prepared by: coating the polymer solution on a non-woven fabric by a doctor blade, and forming a polymer film from the polymer solution by a phase inversion method to prepare the non-woven fabric coated with the polymer film by the doctor blade;

preferably, the polymer is polyacrylonitrile, polyethersulfone, polysulfone, polyimide, polyamide, polyetherimide, polyamideimide, cellulose acetate, cellulose triacetate, or polyvinylidene fluoride;

preferably, the phase-inversion conversion liquid is deionized water, a tannin coagulation bath, an aqueous sodium hydroxide solution, absolute ethanol or absolute methanol.

The invention adopts a solution method, can optimize the prepared polydimethylsiloxane composite membranes with different crosslinking densities by controlling the addition amount of the crosslinking agent, and achieves the regulation and control of the membrane separation performance, thereby leading the viscoelastic membrane with low crosslinking density to have higher permeation flux and excellent ethanol/water separation factor.

The polymer/non-woven fabric support layer is a microfiltration membrane or an ultrafiltration membrane, and during preparation, a polymer solution is coated on the non-woven fabric by scraping, and then a phase conversion method is carried out to prepare the porous support layer, wherein the mass concentration of the polymer solution is 10-20 wt%. The conversion liquid for phase conversion of the polymer/non-woven fabric support layer is selected from one or more of secondary water, tannin coagulation bath, sodium hydroxide water solution, anhydrous ethanol and anhydrous methanol.

The following are specific comparative examples and examples:

comparative example 1

The polymer/non-woven fabric support layer of the composite membrane of this comparative example was a polyvinylidene fluoride/non-woven fabric microfiltration membrane. The preparation process of the composite membrane comprises the following steps:

(1) preparing a vinyl-terminated polydimethylsiloxane normal hexane solution with the mass fraction of 20 wt%, and completely dissolving the vinyl-terminated polydimethylsiloxane normal hexane solution under the condition of stirring at room temperature to obtain a uniform vinyl-terminated polydimethylsiloxane solution.

(2) Adding a crosslinker and a catalyst to a vinyl terminated polydimethylsiloxane solution, vinyl terminated polydimethylsiloxane: poly (methylhydrogensiloxane) (crosslinker): chloroplatinic acid (catalyst) mass ratio of 100: 10: stirring at room temperature, scraping the solution on a polyvinylidene fluoride/non-woven fabric microfiltration membrane for solidification to form an elastic membrane when the viscosity of the solution is increased.

Comparative example 2

(1) preparing a hydroxyl-terminated polydimethylsiloxane normal hexane solution with the mass fraction of 20 wt%, and completely dissolving the solution under the condition of stirring at room temperature to obtain a uniform hydroxyl-terminated polydimethylsiloxane solution.

(2) Adding a crosslinker and a catalyst to a hydroxyl terminated polydimethylsiloxane solution, hydroxyl terminated polydimethylsiloxane: tetraethoxysilane (crosslinker): dibutyltin dilaurate (catalyst) mass ratio 90: 10: stirring at room temperature, scraping the solution on a polyvinylidene fluoride/non-woven fabric microfiltration membrane for solidification to form an elastic membrane when the viscosity of the solution is increased.

Example 1

Respectively preparing a trimesic acid chloride and an amino-terminated polydimethylsiloxane normal hexane solution, wherein the mass fraction of the trimesic acid chloride in the trimesic acid chloride normal hexane solution is 0.1 wt%, and the mass fraction of the amino-terminated polydimethylsiloxane in the amino-terminated polydimethylsiloxane normal hexane solution is 10 wt%. 2.7g of 0.1 wt% n-hexane solution of trimesoyl chloride was added in portions to 12.5g of 10 wt% n-hexane solution of amino-terminated polydimethylsiloxane, and after the viscosity of the solution increased, it was knife-coated onto a polyvinylidene fluoride/nonwoven microfiltration membrane to solidify it into a viscoelastic film.

Example 2

The operation was conducted in the same manner as in example 1 except that an amount of 0.1% by weight of a n-hexane solution of trimesic acid chloride was changed to 2.9 g.

Example 3

The operation was conducted in the same manner as in example 1 except that the amount of 0.1% by weight of a pyromellitic trichloride n-hexane solution added was 3.1 g.

Example 4

The operation was conducted in the same manner as in example 1 except that the amount of 0.1% by weight of a pyromellitic trichloride n-hexane solution added was 3.3 g.

Example 5

The operation was conducted in the same manner as in example 1 except that the amount of 0.1% by weight of a pyromellitic trichloride n-hexane solution added was 3.4 g.

Example 6

The operation was conducted in the same manner as in example 1 except that the amount of 0.1% by weight of a pyromellitic trichloride n-hexane solution added was 3.5 g.

Example 7

Preparing a hydroxyl-terminated polydimethylsiloxane normal hexane solution, wherein the mass fraction of the hydroxyl-terminated polydimethylsiloxane in the hydroxyl-terminated polydimethylsiloxane normal hexane solution is 20 wt%. 0.01g of ethyl orthosilicate and 0.01g of dibutyltin dilaurate are added into 5g of 20 wt% hydroxyl-terminated polydimethylsiloxane n-hexane solution, and after the viscosity of the solution is increased, the solution is blade-coated on a polyvinylidene fluoride/non-woven fabric microfiltration membrane for solidification to form a viscoelastic membrane.

Example 8

The procedure was as in example 7 except that ethyl orthosilicate was added in an amount of 0.0075 g.

Example 9

The procedure is as in example 7, except that ethyl orthosilicate is added in an amount of 0.005 g.

Example 10

The procedure is as in example 7, except that 0.0025g of ethyl orthosilicate is added.

Example 11

Preparing a vinyl-terminated polydimethylsiloxane normal hexane solution, wherein the mass fraction of the vinyl-terminated polydimethylsiloxane in the vinyl-terminated polydimethylsiloxane normal hexane solution is 20 wt%. 0.01g of poly (methylhydrogensiloxane) and 0.001g of chloroplatinic acid were added to a 5g 20 wt% vinyl-terminated polydimethylsiloxane n-hexane solution, which was knife-coated onto a polyvinylidene fluoride/nonwoven microfiltration membrane to solidify it into a viscoelastic film as the solution viscosity increased.

Example 12

The procedure of example 11 was repeated, except that the amount of poly (methylhydrogensiloxane) added was 0.0075 g.

Example 13

The procedure of example 11 was repeated, except that the amount of poly (methylhydrogensiloxane) added was 0.005 g.

Example 13

The procedure is as in example 11, except that the amount of poly (methylhydrogensiloxane) added is 0.0025 g.

The following is a result analysis

FIG. 1 shows the IR spectrum of amino terminated polydimethylsiloxane and viscoelastic composite film of example 3, with the right image being a partial FTIR magnification. In comparison to the amino-terminated polydimethylsiloxane, it can be seen from the partial magnification that example 3 is 1663cm^-1A new peak appears, and the characteristic peak is assigned to the stretching vibration peak of an amido bond (NH-C ═ O). The successful reaction of trimesoyl chloride with amino-terminated polydimethylsiloxane is illustrated.

Table 1 is cross-link density data for comparative example 1, comparative example 2, example 1, example 2, example 3, example 4, example 5, and example 6 viscoelastic composite films. The viscoelastic composite films of examples 1-6 all exhibited lower crosslink densities than the elastic composite films of comparative example 1 and comparative example 2. The crosslinking density of the viscoelastic composite films of examples 1 to 6 gradually increased with the increase in the amount of 0.1 wt% trimesoyl chloride added.

TABLE 1

Fig. 2 is a graph showing the phase angle (δ) and tan δ of the composite films obtained in comparative example 1, comparative example 2 and example 3. As can be seen from the graph, the composite films prepared in example 3 exhibited higher values of tan δ and δ than the composite films prepared in comparative examples 1 and 2. Generally considered as δ being close to 90 °, the material is in a viscous state; δ is close to 0 °, the material is in an elastic state; between which the material is in a viscoelastic state. As can be seen from the figure, the composite film obtained in example 3 exhibited a viscoelastic state, and thus was a viscoelastic composite film; whereas the composite films of comparative example 1 and comparative example 2 had a delta of approximately 0 deg., and were therefore elastic composite films. The main reason for this result is that the composite membrane prepared in example 3 has a lower crosslink density, as shown in table 1.

FIG. 3 shows phase angles (δ) and tan δ of the composite films obtained in example 1, example 2, example 3, example 4, example 5 and example 6. As can be seen, the values of tan delta are from 0.5 to 0.8 and delta is from 30 to 45, indicating that the composite films prepared in examples 1 to 6 are all viscoelastic composite films having a cross-link density in the range of 1.0X 10^-4mol/mL-3.0×10^-4mol/mL (as described in Table 1). This result demonstrates that by controlling the cross-link density of polydimethylsiloxane appropriately, novel viscoelastic composite films can be prepared.

Fig. 4 is the results of the swelling degree test of the composite films of comparative example 1, comparative example 2 and example 3. The viscoelastic composite membrane prepared in example 3 exhibited a greater swelling degree in water, ethanol, and a 5 wt% ethanol aqueous solution, even when the swelling degree of ethanol exceeded 105%, compared to the elastic composite membranes prepared in comparative examples 1 and 2. This result demonstrates that viscoelastic composite membranes have more flexible molecular segments and greater free volume.

Fig. 5 is the results of the pervaporation test on the composite membranes of comparative example 1, comparative example 2 and example 3. The viscoelastic composite membrane prepared in example 3 exhibited higher permeation flux and separation factor, which were improved by 453% and 35%, respectively, compared to the elastic composite membrane prepared in comparative example 1. The viscoelastic composite membrane prepared in example 3 exhibited higher permeation flux and separation factor, which were improved by 66% and 28%, respectively, compared to the elastic composite membrane prepared in comparative example 2. This result is attributed to the lower crosslink density of the viscoelastic composite membrane (as shown in table 1), which makes the molecular chain more flexible, and is more favorable for the permeation of the feed liquid during the pervaporation separation process, thereby showing higher permeation flux.

Fig. 6 is the results of pervaporation tests on viscoelastic composite membranes of example 1, example 2, example 3, example 4, example 5, and example 6. The viscoelastic membranes prepared in examples 1 and 2 exhibited higher permeation flux and lower ethanol/water separation factor, mainly due to lower crosslink density, making the resulting viscoelastic composite membranes defective. The viscoelastic composite membranes prepared in examples 3-6 exhibited relatively stable permeation flux and ethanol/water separation factor, indicating that the crosslink density of examples 3-6 was optimal, ranging from 1.4X 10^-4mol/mL-3.0×10^-4mol/mL。

FIG. 7 is a graph showing the time taken for the viscosity of the casting solutions of comparative example 1, comparative example 2 and example 3 to reach 150 mPas. The time taken for the casting solution of example 3 to reach 150mPa s was about 30 minutes, which was shortened by about 15 times as compared with comparative example 1 and by about 10 times as compared with comparative example 2.

FIG. 8 is the change in viscosity of the casting solution of example 3 with storage time. The casting solutions of comparative examples 1 and 2 could not be stored for a long period of time due to an excess of cross-linking agent, and finally formed solids in about 12 hours. And the casting solution of the example 3 is stored for 75 days, the viscosity of the casting solution is only reduced by 13.1 percent, and the casting solution can still be used for blade coating of a viscoelastic composite film.

Comparative examples 1 and 2 were prepared as elastic composite films, and for comparison with the viscoelastic composite film of the present invention, on the one hand, the preparation of the present invention was illustrated as a viscoelastic film by tan δ and δ; on the other hand, to demonstrate the better separation performance of my viscoelastic composite membrane over an elastic membrane.

FIG. 9 is a graph of the effect of post-treatment temperature on pervaporation performance after preparation of viscoelastic composite films according to example 3. As can be seen from the figure, the permeation flux and the ethanol/water separation factor are not substantially changed with the increase of the post-treatment temperature, which indicates that the post-treatment temperature has no obvious influence on the pervaporation performance, and the trimesic acid chloride has high reactivity and almost completely participates in the crosslinking reaction, and even if the post-treatment is continuously heated, the influence on the crosslinking density of the viscoelastic composite membrane is not obvious, so that the pervaporation performance is not obviously influenced. This result demonstrates that no post-heat treatment of the viscoelastic composite film is required, reducing energy consumption for preparation.

According to the test results, the high-performance composite membrane is prepared by directly adopting a simple solution blending method without other modification means, and the membrane preparation process is greatly simplified.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A preparation method of a viscoelastic composite membrane is characterized in that polydimethylsiloxane is dissolved in an organic solvent, and then a cross-linking agent is added to enable the polydimethylsiloxane to carry out a cross-linking reaction; the addition amount of the cross-linking agent is controlled to ensure that the cross-linking density of the polydimethylsiloxane is low, so as to obtain the low cross-linking density polydimethylsiloxane viscous solution, wherein the low cross-linking density is 1 multiplied by 10^-4mol/mL-3×10^-4mol/mL; and (3) coating the low crosslinking density polydimethylsiloxane viscous solution to a supporting layer by blade coating, and volatilizing an organic solvent to obtain the viscoelastic composite membrane.

2. The method of preparing a viscoelastic composite film according to claim 1 wherein the phase angle of the viscoelastic composite film is between 15 ° and 75 °.

3. The method of preparing a viscoelastic composite film according to claim 2 wherein the phase angle of the viscoelastic composite film is in the range of 30 ° to 45 °.

4. The method of claim 1, wherein the polydimethylsiloxane is an amino-terminated polydimethylsiloxane, the cross-linking agent is a monomer containing an acid chloride group, and the monomer containing an acid chloride group is dissolved and added to the amino-terminated polydimethylsiloxane solution; the mass ratio of the amino-terminated polydimethylsiloxane to the monomer containing the acyl chloride group is (350) -470) 1;

5. The method of preparing a viscoelastic composite membrane according to claim 1 wherein the polydimethylsiloxane is hydroxyl-terminated polydimethylsiloxane, the crosslinking agent is a silane coupling agent containing ethoxy or methoxy groups, and the catalyst for the crosslinking reaction is dibutyltin dilaurate; the mass ratio of the hydroxyl-terminated polydimethylsiloxane to the silane coupling agent is (99-399) to 1;

6. The method of claim 1, wherein the polydimethylsiloxane is a vinyl terminated polydimethylsiloxane, the cross-linking agent is a siloxane containing silicon-hydrogen bonds, and the catalyst for the cross-linking reaction is chloroplatinic acid or [1, 3-dicyclohexyl-imidazol-2-yl ] [1, 3-divinyl-1, 1,3,3, -tetramethyldisiloxane ] platinum (0); the mass ratio of the vinyl-terminated polydimethylsiloxane to the siloxane containing the silicon-hydrogen bond is (99-399) to 1;

7. A viscoelastic composite film prepared according to any one of claims 1 to 6.

8. The viscoelastic composite film of claim 7 wherein the viscoelastic composite film comprises a support layer and a viscoelastic selective layer, the viscoelastic selective layer being knife coated onto a surface of the support layer; the viscoelastic selective layer is polydimethylsiloxane with low crosslinking density, specifically 1 × 10^-4mol/mL-3×10^-4mol/mL; the supporting layer is a polymer film, or the supporting layer is non-woven fabric coated with the polymer film in a scraping mode, or the supporting layer is an inorganic film.

9. Use of the viscoelastic composite membrane according to claim 7 or 8 for separating an organic solvent from a mixed solvent miscible with water.

10. The use of claim 9, wherein the water-miscible organic solvent is ethanol, methanol, isopropanol, ethyl acetate, acetone, ethylene glycol or butanol;

preferably, the temperature of the separation is 30 ℃ to 80 ℃;